This invention relates to a wire brake for robotic welding torch. Specifically the present invention is used to improve the accuracy of the joint-finding processes which use the wire electrode as a probe. This process is generally known as "touch-sensing" or "seam-finding". The term "wire brake" refers to a clamping device which holds the wire electrode stationary relative to the probe during the touch sensing process.
Typical robotic welding torches include a torch having a longitudinal bore extending therethrough. Within the bore is an elongated electrode wire which protrudes outwardly a short distance form the lower end of the torch, and which also protrudes from the upper end of the torch to a wire feed system. The wire feed system feeds the wire through the torch as the wire is being consumed during the welding process.
The wire extends through a flexible cable from the drive system to the torch. Inside the cable the wire is guided to the torch by a flexible liner usually made of coiled steel or nylon. The inner diameter of the liner is slightly larger then the outer diameter of the wire so that the wire can slide easily through the cable.
During the touch-sensing or seam-finding action, the electrode wire is charged with a voltage. The robot then moves the electrode toward a surface of the work piece. When the electrode contacts the work piece, that contact causes the electrode voltage to discharge. This phenomenon is detected by the robot control and the location of the surface is memorized. The robot can then detect and memorize the locations of multiple surfaces and this data can be used for mathematical calculation of the location of weld joints between the surfaces. The robot can then deliver the electrode exactly to the joint to perform the optimal welding. This type of joint locating method is common in the robotic welding industry.
A problem that frequently occurs with this method is lost motion of the weld wire during movement of the robot and the welding torch. In order to achieve accurate position information, the "stick out" of the electrode is critical. By "stick out" is meant the distance that the electrode wire protrudes from the lower end of the welding torch. During normal movement of the torch by the robot, the weld wire is alternatively tightened and slackened in the flexible liner, and this causes the end of the wire to move in or out with respect to the lower end of the weld torch. The accuracy of the surface detection is therefore compromised. In many cases this lack of accuracy makes robotic technology unusable for some applications.
Wire brakes have been used to secure the wire rigidly to the torch during the seam-finding or touch-sensing action. These prior art devices usually require two actions. One action "brakes" the wire close to the welding torch which prohibits the lost motion from translating to the end of the wire. The other action releases the drive roll tension from the wire to allow the wire to move freely in the cable liner. The releasing action is required because the drive roll tension in prior art devices is stronger then the braking resistance at the torch. Once these two actions are taken the wire end remains in the same position with respect to the torch when the robot moves the torch. When actually welding, the wire brake is released, and the drive rolls are tensioned so as to feed the wire during the welding process.
Many prior art wire brakes include an actuator mounted on the outside of the torch housing. These brake actuators are so large that they interfere with the welding in many situations. The size and the position of the actuator can prevent the robot from positioning the torch for optimal welding.
Welding torches and torch components are consumables in the arc welding process. They are used for both manual and automatic applications. Current wire brake systems are brand and model specific, which inhibits the potential advantage of being able to interchange consumable parts.
Wire brakes presently known in the prior art require custom designed systems, including robotic systems that have wire drivers which are capable of releasing at the same time that the wire brake is actuated. Many wire drive systems are not readily adaptable to this releasing action, and therefore are not adaptable for use with a presently known wire brakes.
Therefore a primary object of the present invention is the provision of an improved wire brake for robotic welding torch.
A further object of the present invention is the provision of an improved wire brake which permits holding the wire securely to the welding torch without the need for releasing the drive rollers at the same time.
A further object of the present invention is the provision of a wire brake which can be applied to different makes and models of welding torches.
A further object of the present invention is the provision of an improved wire brake which protrudes a minimum distance from the welding torch so as to minimize interference with movement of the welding torch during the welding process.
A further object of the present invention is the provision of an improved wire brake which can be fitted within the cylindrical housing of a welding torch.
A further object of the present invention is the provision of an improved wire brake which can be easily assembled and adapted to various types of welding torches.
A further object of the present invention is the provision of an improved wire brake which is economical to manufacture, durable in use and efficient in operation.